feat(web): extend ArtistRef/AlbumRef + add HomePayload + new query keys

Adds sort_name/cover_url to ArtistRef, sort_title to AlbumRef (matching
backend Task 5 wire shape), HomePayload type, and qk.home/albumsAlpha/
artistTracks query keys. Updates existing test fixtures to satisfy the
new required fields.

Verified clean via 'npm run check' (0 errors, only pre-existing warnings).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/routes/library/liked/liked.test.ts

@@ -42,9 +42,9 @@ afterEach(() => vi.clearAllMocks());
 
 describe('liked library page', () => {
   test('renders three sections when each has items', () => {
-    const ar: ArtistRef = { id: 'a1', name: 'X', album_count: 1 };
+    const ar: ArtistRef = { id: 'a1', name: 'X', sort_name: 'X', album_count: 1, cover_url: '' };
     const al: AlbumRef = {
-      id: 'al1', title: 'Y', artist_id: 'a1', artist_name: 'X',
+      id: 'al1', title: 'Y', sort_title: 'Y', artist_id: 'a1', artist_name: 'X',
       year: 2020, track_count: 1, duration_sec: 100, cover_url: '/x'
     };
     const tr: TrackRef = {